Question / Help Quicksync Sudden Lag Issue

[Fluffyrox4]

So I'm using Quicksync to try and record some videos. The only problem is, when I record, it becomes really, REALLY laggy. It starts fine, but suddenly gets bad a little into the video. I am getting no lag in game too, just in the recording.

My settings are:
ADVANCED
Encoder: Quicksync H.264
Target Usage: balanced
Profile: high
Keyframe Interval: 2
Async Depth: 5
Rate Control: CBR
Bitrate: 5000

Here's a link to the footage I filmed:
https://www.youtube.com/watch?v=oGc4BEQhMGE&feature=youtu.be

I've also included a log of the above recording. I also run Win10 on a Lenovo ideapad520.

Any help would be appreciated.

Thanks!